Converting to and from display/sim units.

I was messing around with Farseer, and I noticed that when I would set the position of a sprite, it would not end up where expected. I also noticed that the gravity seemed off. I did some research and found some information about converting the value to
display units. I tried, and it works right...but I was just curious about something.

Here's an example of a property I made to store the position of the sprite: